1. Field of the Invention
The present invention relates to an IP telephone system, an IP telephone apparatus and a method for identifying destination user.
2. Description of Related Art
The recent rapid growth of the Internet has drawn attention to an IP telephone system that enables low-cost voice communications with telephone apparatuses at remote places as well as free voice communications between IP telephone apparatuses owned by subscribers. Among such IP telephone systems, there is a proposal for an IP telephone system that allows the transmitting party to specify a screen display or ring tone on the receiving party's end for the purpose of improving user convenience (See Related Art 1, for example).
On the other hand, as an underlying technology, ENUM is emerging as the focus of attention, enabling communications according to individual user circumstances by effectively controlling information used for various communications tools including telephones, facsimiles, mobile phones and electronic mails. ENUM is designed to identify the Internet service with a unique global identification number such as the E. 164 number, using the DNS (Domain Name Server). Currently, the IETF (Internet Engineering Task Force) is seeking to standardize ENUM platforms, where protocol specifications are discussed (See Publication 1, for example).                [Related Art 1] Japanese Laid Open Publication 2003-188992        [Publication 1] Issued by ENUM Trial Japan “ENUM Trial Japan First Report” May, 2004        
However, the above-described conventional IP telephone system only allows the transmitting party to specify, according to the caller's circumstances, operations performed on the receiving party's end, such operations relating to the screen display or the ring tone when a call is received. The conventional IP telephone system is not capable of specifying operations according to a call recipient's individual circumstances.
In general, IP telephone apparatuses used in homes or companies are shared by a plurality of users. For a shared IP telephone apparatus, when a user picks up a call intended for another user, it becomes necessary for the user to pass the call to the intended user.